The present invention relates generally to methods add apparatus for actuating tubing conveyed perforating guns to perforate subsurface formations, and more specifically relates to methods and apparatus which allow a tubing conveyed perforating gun to be actuated either mechanically or hydraulically.
Conventional firing heads for tubing conveyed perforating guns are typically actuated by either mechanical means or by hydraulical means. Mechanically-attuated firing heads are typically actuated by dropping a weighted member (commonly known as a "go-devil"), into the well to impact a piston and drive a firing pin into an initiator charge. An example of this type of firing head may be found in U.S. Pat. No. 3,706,344, issued Dec. 19, 1972 to Roy R. Vann, and assigned to the assignee of the present invention. Hydraulically-actuated firing heads typically contain a piston which is exposed on one side to the annulus pressure in the well surrounding the firing head. When the pressure in the annulus exceeds a predetermined actuation pressure, the piston will move and drive a firing pin into an initiator charge.
Additionally, firing heads are known which are actuated by a combination of mechanical action and hydraulic action. For example, a go-devil will be used to impact a striking piston and to move the piston from a first position to a second position. The movement of the striking piston to the second position will release a locking mechanism on a hydraulic piston which will then be moved in response to hydraulic pressure in the annulus to bring a firing pin into contact with an initiator charge. A firing head of this type is disclosed in co-pending application Ser. No. 040,217, filed Apr. 20, 1987 in the names of Flint R. George and Kevin R. George, and assigned to the assignee of the present application.
Well perforating operations take place under a wide variety of environmental conditions which can be extremely severe. Severe or unexpected environmental conditions may cause unexpected problems in satisfactorily performing tubing conveyed perforating jobs. For example, a mechanically-actuated firing head may be obstructed by particulate solids in the well which may prevent its operation. Additionally, factors such as deviation of the well may affect the ability to practically actuate a firing head mechanically. Similarly, it is not always possible to actuate a hydraulic firing head in a particular well. For example, defective or weak casing may make it impractical to apply increased pressure to the annulus to hydraulically actuate a firing head. Accordingly, it is desirable to have alternative methods for actuating the firing head.
Accordingly, the present invention provides a new method and apparatus for actuating a perforating gun. The apparatus allows the perforating gun to be actuated either hydraulically or mechanically. Additionally, a firing head in accordance with the present invention may be adapted to be responsive not only to longitudinal force in a downward direction, such as is accomplished with a weighted member, but also to longitudinal force in an upward direction, as may be applied with a wireline or slickline.